1. Field of Invention
The present invention relates to the field of vertical injection molding machines. More specifically, the invention relates to a mold shuttle system that independently moves a pair of lower mold halves sequentially between an indexed position and an offset position that is near the operator reducing the time between injection cycles and increasing throughput.
2. Related Art
A vertical injection molding machine uses a mold, typically formed of an upper mold half and a lower mold half, that when clamped together form a mold cavity. When an injection molding machine is used in an insert molding procedure, the sides of the mold are to initially separated to allow placement of the inserts in the mold. The mold halves are then clamped together in the vertical injection molding machine. An injection nozzle of the machine engages the mold and injects the material such as plastic into the mold cavity through an injection passageway provided in the mold. The material flows into the mold cavity and hardens forming the part. The halves of the mold are separated and the part is removed from the mold cavity. Typically, one of the mold sides is movable vertically to open the mold and provide for the removal of the molded part between injection cycles. Although either the upper mold half or lower mold half may move, the present application will focus on a machine in which the upper mold half moves vertically to engage the lower mold half of the mold.
During the molding procedure, the typical vertical injection molding machine is idle between injection cycles while the part is removed from the mold cavity and the mold is prepared for the next injection cycle by placing the required inserts in the mold. The longer the time between injection cycles, the lower the throughput and the less efficient the machine.
One manner of reducing the idle time and increasing the throughput is to incorporate a shuttle system into the vertical injection molding machine. Typical shuttle systems are one of two types, a rotary table or a side-to-side shuttle system. In the rotary table shuttle system, two or more lower mold halves of the mold are equally spaced about and are attached to a table of the injection molding machine. The table rotates to sequentially index the lower mold halves beneath the upper mold half for injection. Thus, while one of the lower mold halves, the indexed lower mold half, is beneath the upper mold half, the injection molding machine can clamp the upper mold half to the indexed lower mold half and complete the injection cycle on the completed mold. At the same time, the other lower mold halves are offset from the indexed position and are therefore available for the operator or operator robot to remove the formed part from the mold cavity and prepare the mold for injection. Thus, by adding lower mold halves that are sequentially indexed for injection, the rotary table shuttle system increases the throughput through the system.
One problem associated with rotary table systems is that they are relatively large and require a larger mounting area. Additionally, most of the machines incorporating a rotary system are adapted to use at least four lower mold halves. This requires the construction of four relatively expensive lower mold halves, increasing the tooling costs for each part made using the machine.
In injection molding machines incorporating a side-to-side shuttle systems, the machine has a table that slides side-to-side beneath the injection assembly and the upper mold half. A pair of lower mold halves mounted to the table move with the table. The table slides alternately from one side to the other to sequentially index each of the lower mold halves beneath the upper mold half where the aligned halves are clamped and the injection cycle is completed. During the injection cycle, an operator or robot can access the lower mold half that is offset from the indexed position, remove the part from the mold, and prepare the mold for injection.
However, because the table slides side-to-side, the operator must walk from one side of the table to the other to access the lower mold half that is offset from the injection assembly. The distance between the two positions where the operator can access the lower mold halves is typically about four feet. Often the cycle for preparing a mold, moving the mold into position, injecting the material into the mold, moving the mold to the offset position and removing the completed part is only about ten to fifteen seconds. Therefore, the four foot distance between offset positions is relatively far considering that the operator must walk the distance every cycle. Any delay by the operator reduces the machine's throughput. Although robots can be used to perform some of the preparatory and part removal functions, the side-to-side shuttle system typically requires the use of two robots, one on each side of the injection molding machine.
Additionally, neither the rotary system nor the side-to-side system allows for independent control of individual lower mold halves. Therefore, any damage to or required maintenance on one of the lower mold halves requires that the complete machine be shut down for repair or maintenance.
Thus, despite the use of the prior art features, there remains a need for a shuttle system that increases the throughput of an injection molding machine, that reduces the distance between offset positions, and that provides for independent control of the lower mold halves allowing maintenance to be performed on one while the machine continues to operate with the other lower mold half.